Fuses are widely used in the home and in industrial environments to prevent unacceptably large electrical currents from damaging electrical conductors and equipment. Known fuses typically provide the protective function by destroying a conductive path therein so as to produce an open-circuit condition which effectively disconnects the protected equipment from an electrical source. The designer of electrical fuses, therefore, must consider the operating parameters and conditions of the equipment which is intended to be protected. One such design parameter is the current rating or maximum current which a fuse must conduct without producing a circuit interruption. Another design parameter is the response time, or fusing speed, which may be defined as the time which elapses between the application of an overload current and the interruption of the flow of current by the fuse.
In its most basic form, a fuse contains a somewhat resistive conductive element which is electrically disposed between two electrical terminals which permit interconnection of the fuse in a circuit to be protected. During an overload condition, the heat which is generated by the flow of current through the resistive conductive element causes a material in the element to melt and to vaporize. In a more advanced type of known fuse, commonly referred to as a dual element fuse, two or more conductive elements, along with a mechanism, are serially connected to one another. This known combination precludes premature current interruptions for overloads which are either slight or short lived, such as the starting currents of electrical motors; and yet provides satisfactory open-circuit response to excessive overloads.
The above-described prior art fuse configurations provide satisfactory current protection for heavy electrical equipment. However, such known fuses are generally not suited for protecting circuitry which has a low maximum current rating, and which requires a short response time. Thus, it is a problem with known fuses that they are not generally suitable for protecting semiconductor devices. Indeed, conventional fuses often generate sufficient heat to limit the number of fusinq devices which can be installed in a small enclosure.
It is, therefore, an object of this invention to provide an improved current interruption device which requires less energy to interrupt a current flow in a circuit then conventional fuses.
It is a further object of the invention to provide a current interruption device which contains stored energy, the stored energy being released to interrupt a flow of electrical current upon the occurrence of predetermined thermal conditions.
It is yet another object of the invention to achieve an interruption of an electrical current in a shorter period of time from the application of an overload condition than would be required by a conventional fuse arrangement.